Nested Strain Wave Differential for Redundant High Gear Reduction
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Solution Overview
Problem
Existing actuation systems, such as those in aircraft, require dual motor drives for redundancy, necessitating additional gear components that increase weight, volume, and failure modes due to the need for a differential gear configuration and downstream reduction gear for desired rotational output.
Innovation Solution
A strain wave gear differential with a high gear reduction design incorporating a ground ring, flex splines, input shafts with wave generators, and a circular gear, allowing for counter-rotation and simultaneous or separate rotation of input shafts, and an output shaft that integrates differential and gear reduction functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential gear configuration is used to achieve dual motor drive with redundancy, then reliability is improved, but device complexity and weight increase due to additional gear components
Solution Approach 1:
The patent merges the differential gear mechanism and reduction gear into a single integrated strain wave gear differential unit. The flex splines with dual tooth sets (inverted and conventional) enable both differential function and high reduction ratio in one compact structure, eliminating the need for separate downstream reduction gears and reducing overall device complexity while maintaining redundancy
Solution Approach 2:
The circular gear component performs multiple functions simultaneously: it acts as both a differential element (receiving torque from two input shafts) and a reduction gear (providing high gear reduction through engagement with flex spline tooth sets). This multi-functionality reduces the number of separate components needed while achieving both redundancy and desired rotational output
2Speed
If additional downstream reduction gear is added to achieve desired rotational output, then speed reduction is improved, but weight and volume increase
Solution Approach 1:
The patent combines the reduction gear function within the differential mechanism itself. The flex splines engage with the circular gear through dual tooth sets that provide high reduction ratio (e.g., 10:1 or higher) directly at the differential output, eliminating the need for separate downstream reduction stages and their associated weight
Solution Approach 2:
The patent employs a nested configuration where the second flex spline is positioned radially within the first flex spline, and both engage with the circular gear. This nested arrangement achieves compact packaging of multiple reduction stages within a single integrated structure, minimizing volume and weight while providing the required speed reduction
3Speed
If additional downstream reduction gear is added to achieve desired rotational output, then speed reduction is improved, but volume increases
Solution Approach 1:
The patent merges the differential gear mechanism and reduction gear into a single integrated strain wave gear differential unit. The flex splines with dual tooth sets (inverted and conventional) enable both differential function and high reduction ratio in one compact structure, eliminating the need for separate downstream reduction gears and reducing overall device complexity while maintaining redundancy
Solution Approach 2:
The patent employs a nested configuration where the second flex spline is positioned radially within the first flex spline, and both engage with the circular gear. This nested arrangement achieves compact packaging of multiple reduction stages within a single integrated structure, minimizing volume and weight while providing the required speed reduction
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design provides a high gear reduction in a compact form, optimizing weight, volume, and reliability while ensuring fault tolerance by enabling redundant motive inputs, allowing continued operation even if one motor fails.
Implementation Method 1
a first flex spline extending axially from the ground ring; a first input shaft that is radially exterior to the first flex spline, wherein the first input shaft includes a first wave generator that engages the first flex spline
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A harmonic drive, having: a ground ring (110); a first flex spline (120) extending axially from the ground ring; a first input shaft (SI1) that is radially exterior to the first flex spline, the first input shaft includes a first wave generator (140) that engages the first flex spline; a second flex spline (150), radially within the first flex spline and rotationally coupled to the first flex spline, a second input shaft (SI2) that is radially within the second flex spline, the second input shaft includes a second wave generator (170) that engages the second flex spline; an output shaft (SO) coupled to the second flex spline, the first flex spline includes a first spline (210) that faces radially inward; the second flex spline includes a second spline (220) that faces radially outward; a circular gear (230) having a third spline (240) that face outwardly and engages the first spline; a fourth spline (250) that faces radially inward and engages the second spline.